The present invention relates generally to rotary cutting machines such as drill presses, lathes, and milling machines and the like. The present invention relates more particularly to a method and apparatus for mitigating vibration of spindles, tool holders, and tools associated with such rotary cutting machines, so as to mitigate the occurrence of undesirable chatter and the like caused by such vibration, thereby facilitating use of such rotary cutting machines at enhanced speeds.
Rotary cutting machines such as drill presses, lathes, and milling machines are well known. Such rotary cutting machines are commonly used to cut or remove metal from a workpiece, so as to provide a desired shape to the workpiece. For example, drill presses are typically used to form small to medium size circular openings in a workpiece; lathes are typically used to selectively reduce the diameter of generally symmetric, round workpieces; and milling machines are commonly used to selectively remove material from various shapes of work pieces, including the boring of larger circular openings therein.
Typically such rotary cutting machines are used to perform cutting operations upon metal workpieces. However, those skilled in the art will appreciate that various other materials such as plastics, polymers, and composites, may similarly be shaped. Rotary cutting machines typically comprise a spindle which is caused to rotate by an electric motor or the like. A tool holder attaches to the spindle and is configured to hold the cutting tool which has been selected so as to provide the desired cutting operation upon the workpiece. Generally, such tool holders comprise a central aperture which is configured to receive a shank or elongate shaft portion of the cutting tool. Typically, the tool holder is pulled into the spindle so as to securely hold the cutting tool in place with respect thereto.
Although such contemporary rotary cutting machines have proven generally useful for their intended purposes, the speed with which they operate tends to be undesirably constrained by vibration of the spindle, tool holder, and/or cutting tools associated therewith. More particularly, when either the rotational speed of the cutting tool, the rate at which the cutting tool is advanced with respect to the workpiece, or the depth of the cut being made is increased beyond limits defined by the material of the workpiece, then the cutting tool begins to chatter or vibrate undesirably in a manner which adversely affects the surface finish of the workpiece. Such vibration may also result in more substantial damage to the workpiece and/or the cutting tool if it is permitted to increase in magnitude and/or continues too long.
It will further be appreciated that such vibration of a cutting tool and/or tool holder may result in catastrophic failure of the cutting machine during high speed operations, thereby resulting in potential damage to the workpiece, equipment, and even possible serious injury of nearby personnel.
As those skilled in the art will appreciate, the above mentioned contemporary technique for attaching cutting tools to rotary cutting machines possesses deficiencies which detract from the overall utility of the rotary cutting machine. For example, such attachment of the cutting tool to the tool holder does not assure sufficient concentricity of the cutting tool with respect to the tool holder.
Such a lack of concentricity may result from many factors. For example, dirt, metal shavings, or other contaminants disposed upon either that portion of the cutting tool received within the tool holder or within the bore of the tool holder may cause the cutting tool to be mounted slightly off center. Further, normal manufacturing tolerances of the components of the tool holder may allow slightly off center mounting of the cutting tool.
As those skilled in the art will appreciate, such off center mounting of a cutting tool with respect to the tool holder results in an imbalance of the rotating system defined by the tool holder and the cutting tool. Even a very slight imbalance can cause vibration at high cutting speeds, i.e., high RPM settings of the rotary cutting machine.
As discussed above, such undesirable vibration of the cutting tool causes chatter, thereby resulting in degraded cutting performance, e.g., an undesirable finish of the workpiece and/or reduced cutting speed. Thus, it is desirable to provide for enhanced concentricity of a cutting tool with respect to the tool holder, so as to mitigate such undesirable vibration.
It would further be desirable to provide means for dampening vibration which occurs in the cutting tool and/or tool holder, so as to mitigate the undesirable effects there of. For example, any vibration due to insufficient concentraticity of the cutting tool relative to the tool holder, as well as vibration from any other source, may be dampened so as to reduce the amplitude thereof, thereby mitigating the occurrence of undesirable chatter and facilitating cutting operations at higher speeds.
The present invention specifically addresses and alleviates the above mentioned deficiencies associated with the prior art. More particularly, the present invention comprises a vibration dampened spindle/toolholder assembly comprising a spindle, a tool holder releasibly attached to the spindle for holding a tool, and an annuler dampening member disposed about the tool holder. The annular dampening member is preferably preloaded or compressed intermediate the tool holder and the spindle. The dampening member dampens vibration of the tool holder relative to the spindle so as to facilitate cutting at enhanced speeds. The dampening member dampens such vibration regardless of the cause of the vibration.
Preferably, the dampening member is configured to define an O-ring. The dampening member preferably comprises rubber, a resilient polymer material, or some desired combination thereof. However, those skilled in the art will appreciate that various other resilient materials are likewise suitable.
Optionally, a groove is formed in the tool holder for receiving a first portion of the dampening member. A second portion of the dampening member is compressed intermediate the tool holder and the spindle. Such a groove is particularly suited for use with rotary cutting machines wherein the spindle comprises one or more flanges and the tool holder comprises a corresponding number of cut-outs. In such rotary cutting machines each cut-out receives a flange so as to maintain desired rotation of the tool holder with respect to the spindle, according to well known principles. In this instance, the tool holder preferably comprises a groove formed thereabout, which receives the first portion of the dampening member, thereby causing the dampening member to be recessed sufficiently to mitigate interference between dampening member and the flanges. Thus, the groove prevents the dampening member form being in the way of, e.g., interfering with, the flanges of the spindle when the tool holder is attached to the spindle.
Further, according to the present invention a cutting tool is attached to the tool holder by heating the tool holder and shrink fitting the cutting tool thereto, so as to maintain the desired concentricity of the cutting tool with respect to the tool holder. In this manner, the generation of vibration due to an imbalance of the cutting tool with respect to the tool holder is mitigated.
Further, according to the present invention, the cutting tool comprises an elongate shank having proximal and distal ends, the proximal end is configured to be received within the tool holder and the distal end optionally has an axial bore formed therein for facilitating attachment of a rotary cutting tool thereto. Alternatively, the rotary cutting tool may be permanently formed or affixed to the elongate shank. Optionally, the elongate shank comprises an extension to which the cutting head of the cutting tool is either permanently or removabley attached.
A neck is formed intermediate the proximal and distal ends of the shank. A dampening member is formed about the neck so as to mitigate vibration thereof in a manner which facilitates use of the rotary cutting tool at enhanced speeds.
According to the preferred embodiment of the present invention, the neck has a diameter which is less than the diameter of the remaining portion of the shank, i.e., the proximal and distal ends thereof. As with the dampening member disposed intermediate the tool holder and the spindle, the dampening member formed about the neck of the shank preferably comprises either rubber, a resilient polymer material, or some combination thereof. Those skilled in the art will recognize that other resilient materials are likewise suitable.
According to the preferred embodiment of the present invention, a cover is formed substantially over the dampening material. The cover preferably preloads or compresses the dampening material. The cover preferably comprises a metal cover and preferably extends beyond the neck, along the shank in both the proximal and distal directions, such that it is attached to the wider diameter portions of the shank at either end of the neck thereof. Attachment of the cover to the shank may be performed by shrink fitting the cover thereto, welding the cover thereto, adhesively bonding the cover thereto, brazing, or soldering. When the shank has a sufficiently large diameter, e.g, in excess of three inches, for example, fasteners such as screws, bolts, etc. may be utilized to attach the cover to the shank.
Thus, three separate features of the present invention may be, and preferably are, utilized simultaneously so as to mitigate vibration of a cutting tool and thus facilitate use at enhanced cutting speeds thereof. Thus, the present invention preferably comprises the use of an annular dampening member disposed about the tool holder and compressed intermediate the tool holder and the spindle; a dampening member formed about the neck of the elongate shank of the cutting tool or extension therefor; and the use of a cutting tool which has been shrink fitted to the tool holder. The dampening member disposed intermediate the tool holder and the spindle mitigates vibration of the tool holder relative to the spindle. The dampening member formed about the neck of the shank of a cutting tool or extension therefor mitigates vibration of the shank. The use of a cutting tool which has been shrink fitted to its associated tool holder assures the desired degree of concentricity of the cutting tool with respect to the tool holder, so as to enhance the balance thereof and thereby mitigate vibration of the cutting tool and tool holder.
Since vibration of the tool holder and/or the shank of the cutting tool is readily transmitted to the cutting head, mitigation of vibration of the tool holder and/or the shank of the cutting tool is desirable since it likewise mitigates vibration of the cutting tool.
As those skilled in the art will appreciate, enhancing the cutting speed of such rotary cutting machines similarly enhances the rate at which products are formed therewith. Such an increase in efficiency thus potentially contributes substantially to profitability and is therefore highly desirable.
These, as well as other advantages of the present invention will be more apparent from the following description and drawings. It is understood that changes in the specific structure shown and described may be made within the scope of the claims without departing from the spirit of the invention.